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authorYork Sun <yorksun@freescale.com>2013-03-25 07:40:01 +0000
committerAndy Fleming <afleming@freescale.com>2013-05-24 16:54:10 -0500
commit0aadf4aa51aaf21c62495fb25cc3e76bf0f268c2 (patch)
tree114a9f4b5f201b1a15d38558884a37827a046ce7 /doc
parent0c9ab437de1bcfd0524217619937b162273e43d4 (diff)
powerpc/t4240qds: Add VDD override
Allow VDD voltage overriding with a command. This is an add-on feasture of VID. To override VDD, use command vdd_override with the value of voltage in mV, for example vdd_override <voltage in mV, eg. 1050> The above example will set the VDD to 1.050 volt. Any wrong value out of range of 0.8188 to 1.2125 volt or invalid string is ignored. In addition to the command, if overriding VDD is needed earlier in booting process, save an variable and reboot: setenv t4240qds_vdd_mv <voltage in mV> saveenv Signed-off-by: York Sun <yorksun@freescale.com> Signed-off-by: Andy Fleming <afleming@freescale.com>
Diffstat (limited to 'doc')
-rw-r--r--doc/README.t4240qds24
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diff --git a/doc/README.t4240qds b/doc/README.t4240qds
index 677d120a80f..19e8a8ae1f6 100644
--- a/doc/README.t4240qds
+++ b/doc/README.t4240qds
@@ -96,3 +96,27 @@ The addresses in brackets are physical addresses.
0x0_ffff_f000 (0x0_7fff_fff0) - 0x0_ffff_ffff 4KB Boot page translation for secondary cores
The physical address of the last (boot page translation) varies with the actual DDR size.
+
+Voltage ID and VDD override
+--------------------
+T4240 has a VID feature. U-boot reads the VID efuses and adjust the voltage
+accordingly. The voltage can also be override by command vdd_override. The
+syntax is
+
+vdd_override <voltage in mV>, eg. 1050 is for 1.050v.
+
+Upon success, the actual voltage will be read back. The value is checked
+for safety and any invalid value will not adjust the voltage.
+
+Another way to override VDD is to use environmental variable, in case of using
+command is too late for some debugging. The syntax is
+
+setenv t4240qds_vdd_mv <voltage in mV>
+saveenv
+reset
+
+The override voltage takes effect when booting.
+
+Note: voltage adjustment needs to be done step by step. Changing voltage too
+rapidly may cause current surge. The voltage stepping is done by software.
+Users can set the final voltage directly.